In the field of medical engineering as well as for equilibrium studies, it is important to determine the torsion of the human eye, i.e. the rotation of the eye around the viewing direction (z-axis). In medical engineering, for example for the insertion of toric intraocular lenses, the rotation of the eye must be known exactly in order to ensure the exact adjustment of the lens in relation to the eye. But also for a laser treatment of the eye or its preparation, the knowledge of torsional movements of the eye leads to a more precise result. Further possible fields of application include neuroscience research or investigations of the effect of images or visual stimulations on the human being, for example in the field of advertisement and communications.
Document DE102006002001 describes a method for determining the spatial relationship of an eye with reference to a camera device, in which a model of the eye is constructed and a reference relation of the eye model is determined by using a reference image of the eye. Thereafter position and rotation coordinates are determined by adapting the eye model to a current image of the eye. The eye model comprises texture information which is stored as a feature template map. Features of the feature template map are blood vessels, iris characteristics, limb, limb centre, pupil centre, pupil edge and artificial markers. However, the creation and adaptation of eye models is complex and requires high processing power and corresponding computation time.
When determining the torsion from images of the eye which are taken by a camera, there exists particularly the problem that in addition to the rotation, the image regions may have different sizes and may be out of alignment. This complicates the detection of corresponding image regions.